gsminmag Mineralogical Magazine Mineralogical Magazine 0026-461X Mineralogical Society 10.1180/minmag.1964.033.265.03 Conical Extinction Curves: A New Universal Stage Technique1 Joel N. M.Sc., Ph.D., A.Inst.P. Centro de Investigaciones de Cristalografía, Instituto de Física y Matemáticas, Universidad de Chile, Casilla 2777, Santiago, Chile Tocher F. E. B.Sc., Ph.D. Dept. of Geology and Mineralogy, University of Aberdeen, Aberdeen, Scotland.

This technique was evolved independently and almost simultaneously by the two authors who have agreed on a joint presentation.

 6 1964 33 265 853 867 Copyright © 1964, The Mineralogical Society 1964 Summary

New generalized extinction curves, derived from wave-normals located on a circular cone, are presented. They may be used with the universal stage for the accurate location of up to all three of the indicatrix axes, α, β, γ, of any biaxial crystal, or the optic axis of any uniaxial crystal.